Phthalocyanine compounds are useful as materials for paint compositions, printing inks and catalysts and as electronic materials and, in particular, they have been broadly investigated as materials for electrophotographic photoreceptors, materials for optical recording and materials for photo-electric conversion in these days.
Regarding electrophotographic photoreceptors, recently, the demand for extending the light-sensitive wavelength range of organic photoconductive materials which have heretofore been proposed up to the near infrared wavelength range of semiconductor lasers (780 to 830 nm) so as to use the materials as a photoreceptor for a digital recording system such as a laser printer. From the viewpoint, squalilium compounds (as disclosed, e.g., in JPA-49-105536 and JP-A-58-21414, triphenylamine trisazo compounds (as disclosed, e.g., in JP-A-61-151659) and phthalocyanine compounds (as disclosed, e.g., in JP-A-48-34189 and JP-A-57-148745) have been proposed as photoconductive materials for semiconductor lasers. (the term "JP-A" as used herein means an "unexamined published Japanese patent application")
Where organic photoconductive materials are used as light-sensitive materials for semiconductor lasers, they are needed to satisfy the conditions that the light-sensitive wavelength range is extended up to a long wavelength range and that the sensitivity and durability of the photoreceptors to be formed therefrom are good. The above-mentioned organic photoconductive materials do not sufficiently meet the conditions.
In order to overcome various drawbacks of the known photoconductive materials, the materials have been investigated with respect to the relationship between the crystal form and the electrophotographic characteristics. In particular, many reports relating to phthalocyanine compounds have heretofore been disclosed.
In general, it is known that phthalocyanine compounds have various crystal forms, depending upon the difference in the manufacture method and treating method, and that the difference in the crystal form has a great influence on the photo-electric conversion characteristics of phthalocyanine compounds. Regarding crystal forms of phthalocyanine compounds, for example, with respect to copper phthalocyanine, various crystal forms of .alpha., .pi., .chi., .rho., .gamma., and .delta. are known in addition to a stable crystal form of .beta.. It is also known that these crystal forms are mutually transferable to each other by mechanical strain force, sulfuric acid treatment, organic solvent treatment or heat treatment (as described, e.g., in U.S. Pat. Nos. 2,770,029, 3,160,635, 3,708,292 and 3,357,989). JP-A-50-38543 describes the relationship between the difference of crystal forms of copper phthalocyanine and the electrophotographic characteristics of them.
Regarding the relationship between the crystal forms of hydroxygallium phthalocyanine and the electrophotographic characteristics of them, JP-A-1-221459 mentions crystals obtained by an acid-pasting method.
However, not only the above-mentioned hydroxygallium phthalocyanine crystals but also phthalocyanine compounds which have heretofore been proposed are not sufficient in point of the light sensitivity and the durability when used as a light-sensitive material.
In addition, when hydroxyallium phthalocyanine crystals are used in the form of a dispersion in a binder resin, the crystals are inferior in the dispersibility and the coatability of the dispersion. Where the crystals are used as a photoreceptor, they have problems on the light-sensitivity and the charge retentiveness. Further, they often cause drawbacks of fog or black spots in images formed. Thus, the crystals do not have sufficient characteristics.
Therefore, development of novel crystals of phthalocyanine compounds, which have improved characteristics of light sensitivity, durability, charge retentiveness, coatability and image quality with still having the intrinsic favorable characteristics of the compounds of themselves as a photoconductive material, has been desired.
The present invention has been made in view of the above-mentioned situation.